An electroluminescence device (hereinafter called "EL device") is characterized in exhibiting high visibility due to self-emission and in having excellent impact resistance because of being completely solid. At present, variable EL devices using an inorganic or an organic compound as the emitting layer are proposed and attempts have been made to put them to practical use. One of the EL devices which has been realized is applied as a multi-color light emission apparatus.
Such a multi-color light emission apparatus includes an apparatus produced by combining a color filter of three primary colors (red, green, and blue) with a white-light emitting inorganic EL device and an apparatus produced by patterning inorganic EL devices of three primary colors in order to position the EL devices of three primary colors separately on the same plane and thereby to emit light (Semicond. Sci. Technol. 6 (1991) 305-323) However, there is the problem that the effect of emitting light of each color is limited to 33% of the white light at most if the white color is resolved by the color filter of three primary colors. Further, EL devices which themselves can efficiently emit white light have still not been attained at present.
On the other hand, a photolithography process is used for patterning EL devices. However, it is known that the efficiency and stability of EL devices are greatly reduced in such a wet process.
It is common knowledge that, among EL devices, organic EL devices are promising as highly intense and efficient light emitting devices. In particular, because the light emitting layer is an organic layer, it is highly probable that various emitting colors are produced by the molecular design of organic compounds. Such an organic EL device is expected to be one device which can be used in practice in a multi-color light emitting apparatus.
However, these organic EL devices have the drawback that chemical factors such as external steam, oxygen, organic compound gas, and the like cause deterioration of the EL devices such as reduction in luminance accompanied by the occurrence of dark spots and the like and these devices tend to be destroyed from physical (mechanical) factors such as heat, impact, or the like since the EL devices are composed of a laminate of low molecular organic compounds.
Therefore, the method for separately disposing each of the organic EL devices, which emit lights of three primary colors (RGB), on the same plane can be used in a wet process or a process including heat treatment such as a photolithography process only with difficulty.
In order to solve such a problem, disclosed is a color EL display apparatus (see Japanese Patent Application Laid-open No. 40888/1989). This apparatus is, as shown in FIG. 8, characterized in that an EL emitting layer 1b sandwiched between a lower electrode 1c and a light transmitting upper electrode la is disposed on a substrate 2, the EL light which is output via the light transmitting electrode la is externally output from a transmitting substrate 8 via a color filter 9 installed on the transmitting substrate 8, the color filter 9 facing the transmitting electrode 1a.
This apparatus has, however, the disadvantage that the luminance of the light of each color is reduced to one third of the EL light by the color filter. Also, because the EL device faces the color filter, the light emission life of the EL device is invariably reduced by aqueous vapor, oxygen, gas from organic monomers, low molecular components, and the like generated by the color filter.
To solve these problems, lately disclosed is a technique in which a fluorescent layer absorbing light emitted from an organic EL device and emitting visible fluorescent light is installed in the position (laminated or in parallel) corresponding to the emitting portion of the organic EL device (see Japanese Patent Application Laid-open No. 152897/1991). This technique ensures that the light of a blue or blue-green color emitted from the organic EL device is converted into a fluorescent light which is visible light of a longer wave length. This technique is utilized in a multi-color (three primary colors) light emission apparatus in which fluorescent layers capable of converting the blue or blue-green color into a green or red color are separately disposed on a flat plane (see Japanese Patent Application Laid-open No. 258860/1993).
The installation of the fluorescent layer has the advantage that multi-color light emission which is higher in efficiency than in the case of installing a color filter is expected. Specifically, if the fluorescent layer especially for converting into a green color is expected to absorb 80% or more of the blue color light emitted from the organic EL device, a variety of fluorescent materials capable of emitting fluorescent light at an efficiency of 80% or more are known. Assuming both the light absorbing efficiency and light emitting efficiency of the fluorescent layer to be 80%, it is estimated that the blue light of the organic EL device can be converted into visible light with a long wave length at a yield of 64%.
A multi-color light emission apparatus can be realized using an organic EL device and a fluorescent layer in the above manner. Japanese Patent Application Laid-open No. 258860/1993 proposes the following structure for the multi-color light emission apparatus.
As shown in FIG. 15, fluorescent layers 3R, 3G absorbing the light emitted from an organic EL device and emitting a green color and red color respectively are separately disposed on a transparent substrate 11 on the same plane. A polymer and/or cross-linking compound of an organic monomer or oligomer and a transparent insulating rigid plane layer (protective layer) 7 produced by a sol-gel glass method are laminated on the transparent substrate 11 including the fluorescent layers 3R, 3G by spin casting. A transparent electrode 1a of the organic EL device is disposed on the plane layer 7.
Disclosed as other structures are a structure in which the transparent and insulating flat rigid elements is simply placed on the surface of the fluorescent layer instead of being laminating on the fluorescent layer by spin casting and a structure in which the fluorescent layer is affixed to the back face of the hard element exhibiting the functions of a flat plane layer instead of affixing the fluorescent layer to the surface of the substrate. However, it is reported that the structure shown in FIG. 15 is preferable.
The structure shown in FIG. 15, however, has the problem that the light emission life of the organic EL device is reduced by aqueous vapor, oxygen, gas from monomers and the like which are adsorbed to or included in the organic compound of the flat plane layer in a slight amount whereby the emission is indispensably non-uniform, because the transparent electrode of the organic EL device is only disposed on the same flat layer composed of the polymer and/or cross-linking compound of an organic monomer or oligomer.
Also, a high temperature treatment at 400.degree. C. or more is generally required for the production of the flat plane layer in the sol-gel glass method. This causes the deterioration of the organic fluorescent layer. If the sol-gel glass flat plane is produced by heat treatment (up to the maximum temperature of around 250.degree. C.) which never causes the fluorescent member to deteriorate, there is the problem that the light emission life of the organic EL device is greatly reduced for the same reason as above because water or organic compounds remain.
Also, clear explanations about the hard member in the other structures are not necessarily sufficient.
On the other hand, disclosed is a method in which a glass plate with a color filter formed by printing is disposed under the back face of a glass substrate of an inorganic EL device (see Japanese Patent Application Laid-open No. 119494/1982).
However, a reduction in the emitting efficiency caused by the color filter is easily predicted in this method. Also, since the organic EL device is produced independently of the color filter, camber and distortion of the substrate occur so that the EL device cannot be manufactured in a stable manner, if, for example, the thickness of the substrate of the organic EL device is not increased (around 700 .mu.m or more). As a result of the increase in the thickness of the substrate, the gap between the color filter and the EL device increases, whereby emitted light of a color other than the desired emitted colors leaks to remarkably narrow the angle of view when multi-color light is emitted.
This invention has been achieved in view of this situation and has an object of providing a multi-color light emission apparatus using an organic EL device having superior light emission life and excellent characteristics in the angle of view and a method for manufacturing the multi-color light emission apparatus in a stable and efficient manner.